Abstract The solar system is moving through the interstellar medium with a velocity of about 20 km/s. The neutral interstellar gas, which thereby penetrates the heliosphere, is subject to ionization by solar UV radiation, charge exchange with the solar wind, and electron collisions. The newly created ions are then picked up by the solar wind through interaction with the interplanetary magnetic field. Model descriptions of the interaction with the solar wind are reviewed in this report. While most of the constituents are already ionized far beyond the orbit of the earth, neutral helium (because of its high ionization potential) approaches the sun to < 1 AU. Recently, the pick-up of interstellar He+ ions has been directly observed for the first time. The observed velocity distribution of He+, extending up to double the solar wind velocity, can be explained in terms of pitch-angle scattering of the ions by interplanetary Alfvén waves and subsequent adiabatic cooling in the expanding solar wind. Thermal coupling of the He+ to the solar wind is negligible. Detailed studies of the pick-up distribution provide a method to investigate the interplanetary propagation parameters and the state of the local interstellar medium.
Pick-up of interstellar neutrals by the solar wind
Advances in Space Research ; 6 , 1 ; 199-208
1986-01-01
10 pages
Article (Journal)
Electronic Resource
English
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